With the advent transverse engines and front wheel drives in motor vehicles, various problems have arisen, one of which is that there is less space available in the area within the engine compartment that has in the past been reserved for the steering gear assembly. One solution to this problem has been to move the steering gear rearwardly, but this can mean that in a vehicle fitted with power-assisted steering gear, the hydraulic control valve is located within the cab or passenger compartment. This arrangement has clear disadvantages and it has been proposed to provide axial-displacement hydraulic control valves at a position remote from the steering input to the steering gear assembly. Thus, in the case of a rack and pinion gear, it has been proposed to locate the power assistance axially displaceable control valve on the side of the pinion remote from the steering input with the valve being controlled by a rod which is axially displaceable in response to rotation of the steering input.
This is an advantageous technique for providing additional space rearwardly of the rack bar, but heretofore has not been applicable to power-assisted steering gear assemblies utilising rotary hydraulic control valves. It is established practice that in order to provide the relative rotational movement of the two valve members of a rotary valve, a torsin bar is used and this has the additional advantage of providing the centering effort for the two valve members when there is no rotational movement at the steering input. However, if the torsion bar is extended to accommodate a rotary valve arrangement located at a position remote from the steering input, it has been found that the rotation of the torsion bar at the steering input end is not reflected to any great extent at the valve end because of the length of the torsion bar through which the twisting has to be transmitted, and it is for this reason that in conventional power-assisted steering assembly using a rotary hydraulic valve, the valve means is located on the same side of the assembly as the input shaft, as, for example, in our United Kingdom Patent Specification No. 1,470,975.